#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int my_int(const void* p1, const void* p2) {
	return (int)*(char*)p1 - (int)*(char*)p2;
}
int main()
{
	char arr1[80];
	gets(arr1);
	size_t len1 = strlen(arr1);
	char arr2[80];
	int k = 0;
	for (int i = 0; i < len1; i++) {
		int is = 1;
		for (int j = 0; j < k; j++) {
			if (arr1[i] == arr2[j]) {
				is = 0;
			}
		}
		if (is == 1) {
			arr2[k] = arr1[i];
			k++;
		}
	}
	arr2[k] = 0;
	qsort(arr2, strlen(arr2), sizeof(arr2[0]), my_int);
	printf("%s\n", arr2);
	return 0;
}